An fMRI study of inflectional encoding in spoken word production: Role of domain-general inhibition

A major issue concerning inflectional encoding in spoken word production is whether or not regular forms (e.g., past tense walked) are encoded by rule application and irregular forms (e.g., swam) by retrieval from associative memory and inhibition of the regular rule. We used functional magnetic resonance imaging (fMRI) to examine the involvement of domain-general inhibition, thought to be underpinned by right inferior frontal gyrus (IFG), right pre-supplementary motor area (SMA), and right basal ganglia. Participants switched between producing the past tense of Dutch regular or irregular verbs, or between inflecting or reading the verbs aloud. Compared to reading, inflecting activated left IFG and left preSMA/SMA. Regulars yielded higher activation than irregulars in these frontal areas, both on switch and repeat trials, which did not differ in activation. Switching between inflecting and reading activated left preSMA/SMA. These results indicate that inflectional encoding, and switching between inflecting and reading, are underpinned by frontal areas in the left hemisphere, including left preSMA/SMA for both and left IFG for inflecting, without engaging the domain-general inhibition circuitry in the right hemisphere. We advance an account of inflectional encoding in spoken word production that assumes a distinction between regulars and irregulars, but without engaging domain-general inhibition.